GH-234 text redaction annotation tool

[pcorless]

Initial Support

• allows users to create redaction annotation.
• When the document is exported, corresponding text content is removed from affected document page content streams.

Pending work

• add escape key support to all AnnotationHandlers to make it easier to clear an in-progress annotation.
• Add redaction button to the advance search panel to automatically redact search results.
• Add warning dialog if a document is saved or saved as if redaction annotations are present, basically saying content has not yet been removed.